BMJ said:
I've read on a thread about the CCDB that if you have the HSC circuit wide open that it effects the main shim stacks ability to open properly.
I guess it's like this. If more LSC makes the HSC circuit open sooner, would more HSC make the main shim stack open sooner?
I was thinking of commenting on the CCDB’s somewhat similar LS/HS tuning after looking closely at the Avalanche for my interest in learning more. Thanks for the question!
The Avalanche shocks probably have a shimmed main chamber piston. Below is a diagram of a Penske shock with a most common design using shimmed main piston with a rebound tunable size orifice bypass to tune low speed rebound damping.
There are shims on both sides of the main chamber piston, one set for rebound and one set for compression. I could be wrong about this being the Avalanche design, there’s no diagram I can find for the Avy main chamber, but looking at other similar shock diagrams having LSC/HSC tuning assembly in the flow to the reserve chamber, I have a good huch the Avy is very similarly usiong main piston shims for rebound and probably also for compression.
In the Avalanche (unlike the CCDB and similar RS Vivid) there is a small volume flow into the reserve chamber that is highly “leveraged” by the shaft displacement of fluid from the main chamber during compression, and this flow is restricted and tuned by the LSC/HSC assembly. My guess is that the compression side shims on the main chamber piston produce the main effect of HSC damping in the Avy. I’ll also guess that the LSC screw mainly tunes LSC, and the HSC bolt preloading the spring affects more medium speed transition into high speed damping as well as giving the blow off ability for very sharp big hits, so that high speed damping is mainly damped by the main piston compression shims when the HSC adjustment valve blows open.
Turning both LSC and HSC to max firm in the AVY still allows the HSC adjuster valve to blow open (or the shock would blow up!). When it blows open the main piston shims are all that’s really doing any damping, and the action is probably very platform like loading up the suspension and suddenly digressive or falling rate in “damping” resistance, and very compliant which plunges the travel deeper than a more balanced LSC/HSC tune that produces more linear or rising rate effect in compression resistance.
The CCDB is a high flow system with no main piston dampening shims, except one very firmly preloaded blow off compression shim for the sharpest big hits to avoid high speed flow hydro lock. In the CCDB both compression and rebound LS/HS assemblies appear to be very similar in design to the Avalanche LSC/HSC assembly, except the HS valves in the CCDB appears to use an adjustable spring loaded single shim rather than the Avalanche’s in a HSC tuning/blowoff spring backed piston-like valve with ports allowing tunable transition to blow-off. I’ve included pics of the CCDB adjusters and main chamber twin-tube design diagram after the first diagram of what I think the Avy main chamber is designed similar to.
The CCDB has no internal fine tuning potential. The Avalanche can be fine tuned internally to be more specific for rider weight and use. The Marzocchi World Cup and discontinued ’02 to ’04 Fox Vanilla RC damping are similar to the Avalanche design except there is no HSC external adjuster.